The invention relates to an arrangement for the precise positional joining of a first material web which includes elements of sections having a section length divided by separation locations and a second material web which is provided with marks having a predetermined distance which corresponds to the section length, except possibly for a certain difference. The arrangement includes a first device by which the two material webs are joined, a transport device, by which the two material webs are advanced, stepwise, by the predetermined distance, and a second device by which an element is applied to the first material web when, after the advancing step of the two material webs by a section length, the length of the first material web between the first device and the second device corresponds to a predetermined multiple of the section length plus an offset length which is adjustable by an offset device, and a transport arrangement by which the two material webs can be advanced by the predetermined distance.
With such an arrangement for example so-called blister packages are produced by which for example tablets are distributed and sold. A blister package consists generally of a deep drawing film of plastic or paper including indentations in which the tablets are disposed and which are sealed by a cover foil. The cover foil is generally provided with imprints which generally include information concerning the tablets such as data when and which tablets should be taken. It is therefore very important that this information is applied to the cover foil accurately positioned according to the position of the tablets and consequently the indentations.
Although with modern printing techniques a high accuracy can be achieved, the position-accurate coordination of the imprint on the cover foil with respect to the deep drawing web is highly problematic since any deviations present may be added up. In time, the position of an imprint could deviate from the required position by an intolerable amount. Therefore, printing arrangements have been developed by which the position accuracy of the imprint on the cover foil has been substantially improved. U.S. Pat. No. 5,964,151 for example discloses an arrangement for a position-accurate imprinting of an endless foil without markings, by which imprints of a first predetermined length are applied to a metal foil and, after being imprinted, the foil is cut into sections of a certain predetermined length by a cutting device so that the imprints must be applied to the foil accurately between the cuts.
The known arrangement includes a printer which has an input for initiating a position-accurate printing procedure. Furthermore, there is a sensor which provides at its output a signal when the length of the foil between the cutting device and the location corresponding to the beginning of a section to be imprinted is a predetermined multiple of the second predetermined length.
Since the output of the sensor is connected to the output of the printer the beginning of a foil section to be imprinted is always newly determined. With the constant new determination of the beginning of the section to be imprinted errors possible present cannot be added up. Consequently, even relatively large deviations are generally harmless since errors present in one section do not influence the beginning of the next section to be imprinted.
Furthermore, U.S. Pat. No. 6,164,200 discloses another arrangement for the position-accurate imprinting of an unmarked endless foil, which operates according to the same principle as the printing arrangement described above. The main difference from the above printing arrangement resides in that the endless foil is transported in the earlier mentioned printing arrangement discontinuously whereas in the further printing arrangement the endless foil is continuously transported. However, the printer is also activated whenever the length of the endless foil between the section limit formed by the last cutting and the printing arrangement is a predetermined multiple of the second predetermined length.
Although these known arrangements provide for excellent results, it still has been found that, as a result of external influences, the imprint may be displaced with respect to the location of the indentations. Particularly after a stand-still of the arrangement, deviations sometimes occur, which are no longer tolerable.
U.S. Pat. No. 5,964,970 discloses an arrangement for the position-accurate joining of a first foil, on which elements of an absorbing material are disposed, with a second foil, to which imprint images are applied which include a reference mark. The imprints must correspond to the absorbing elements. The absorbing elements are applied to the first foil which advances at a constant speed, whereby the absorbing elements are disposed on the first foil at a distance from one another which can easily vary. The reference marks or, respectively, the associated imprints are disposed on the second foil at a constant distance from one another, which corresponds to the constant distance at which the absorbing elements of the first foil are arranged.
Before the two foils are joined the second foil is riffled in an apparatus whereby it is shortened. After the second foil has become shorter, it passes through a device in which it can again be stretched. The stretching depends on the position of the absorbing elements disposed on the first foil. With a reduced distance of the subsequent absorbing elements, less stretching takes place than when the elements are arranged at larger distances from one another. With the different stretching of the second foil consequently position displacements of the absorbing elements on the second foil can be corrected.
It is the object of the present invention to provide an arrangement of the type disclosed above in such a way that the position displacements of the elements disposed on the first material web with respect to the marks disposed on the second material web can be reduced.